1. Field of the Invention
The present invention is drawn generally to the field of paper handing systems for printers having photostatic printing systems requiring heated fixing rollers for adhering copy print to the copy media. More particularly, the invention provides a multiple traction source system with individually controllable drive elements to preclude jamming, tearing or skewing of the paper or form while allowing reversible feed capability for reduction of printing media waste.
2. Prior Art
Conventional laser printing systems employ a photoconductive drum activated by a laser to transfer the image to be copied. A transfer unit cooperating with the photoconductive drum deposits toner onto the print medium which is then cured or otherwise affixed to the print medium by a heated fuser assembly. Paper feed systems typically employ a feed roller and idler pair which drives paper through the cooperating photoconductive drum and transfer unit and the fuser assembly is incorporated within a rotating fixing roller which cooperates with a second pressure roller. In typical printing systems to allow the use of cut sheet as the print medium both the feed roller and fixing roller are power driven. Cut sheet is frictionally fed by the feed roller between the drum and transfer unit to the fixing unit. As the sheet reaches the fixing unit it is then also frictionally fed by the fixing roller until the sheet exits the printer.
The prior art printing systems are unsatisfactory for feeding continuous forms in many applications. When a long length or continuous form is frictionally fed simultaneously by two or more rollers, the presence of manufacturing tolerances in the system frequently causes an accumulation of stresses on the form which results in jamming, tearing or skewing. In addition, the presence of a hot fixing roller precludes stopping the paper for any significant period of time due to the potential for scorching. With continuous forms, the sequential nature of the copying process which prints one "document" at a time, cause significant waste of the forms due to the requirement for the last printed form to exit the printer. Unless the paper is then reverse fed to realign the unprinted paper portion with the photoconducting drum, that amount of paper (or forms) is wasted. Normally in printing one document at a time without reverse feeding, wastage of 50% or greater may be present. If reverse feeding is incorporated, the multiple traction point difficulties discussed above are exacerbated.